Method of providing aluminum surfaces with coatings

ABSTRACT

Aluminum articles are produced with a surface coating of highdurability by first electrolytically oxidizing the article in an acidic anodizing bath and after water washing, depositing the article in an aqueous dispersion, emulsion or solution of a thermosetting resin and passing a current through said article as the anode to cause electrodeposition of resin particles in the oxidized porous surface. The article is then heated to cure the resinous film.

United States Patent Inventors Toshiyuki Ohta;

Hisashi Takao, both of Kobe-shi, Japan Appl. No. 861,181 Filed Sept. 25, I969 Patented Nov. 23, I971 Assignee llonny Chemicals Co., Ltd.

Nagata-Ku Kobe, Japan Priority Oct. 15, I964 Japan 39/58326 Continuation-impart of application Ser. No. 494,885, Oct. 11, I965, now abandoned. This application Sept. 25, 1969, Ser. No.

METHOD OF PROVIDING ALUMINUM SURFACES WITH COATINGS [56] References Cited UNITED STATES PATENTS 3,403,088 9/1968 Hart 204/181 3,279,936 l0/l966 Forestek.... 204/38 2,647,079 7/1953 Burnham 204/38 FOREIGN PATENTS l,l48,764 4/ l 969 Great Britain 204/ l 8 l 700,516 l 2/1953 Great Britain 204/38.42 656,566 l/l938 Germany 204/18 l Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews Attorney-Stevens, Davis, Miller & Mosher ABSTRACT: Aluminum articles are produced with a surface coating of high-durability by first electrolytically oxidizing the article in an acidic anodizing bath and after water washing, depositing the article in an aqueous dispersion, emulsion or solution of a thermosetting resin and passing a current through said article as the anode to cause electrodeposition of resin particles in the oxidized porous surface. The article is then heated to cure the resinous film.

METHOD OF PROVIDING ALUMINUM SURFACES WITH COATINGS This application is a continuation-in-part application of Ser. No. 494,885 filed Oct. ll, 1965 now abandoned.

This invention relates to methods of treating aluminum to provide aluminum articles having a surface coating of high durability against corrosion and erosion.

Processes are known for oxidizing aluminum anodically in an electrolyte, such as oxalic acid, sulfuric acid or chromic acid in order to produce a corrosion inhibiting film thereon. These films comprise 'y-Al O and have a porous surface having from about 60 to about 800 of pores per p?- as the electrolytic oxidation, and are normally treated with steam at 4 to 5 atmospheric pressure for between a half and one hour to close the pores therein and turn the film into A1,0,-H,o (Boehmite).

However it is generally not possible to fill every pore of the porous film of y-AI,O in such processes, and on inspection small openings in the pores are still found to remain. Therefore, if acids, alkalis or other corrosive chemicals come into contact with the surface of articles made of such aluminum, the chemicals may penetrate through the film and corrode the aluminum. Thus the aluminum whichhas a surface coating never completely free from defects, exhibits poor resistance to corrosion.

According to the present invention there is provided a method of treating an aluminum article, which comprises anodically oxidizing the surface of the aluminum article in an electrolyte selected from the group consisting of sulfuric acid, chromic acid, oxalic acid and mixtures thereof to form an oxidized film having the thickness of from In. to 2p; immediately after waterwashing, dipping said article in an aqueous dispersion, emulsion or solution of a thermosetting resin; passing through said article as the anode a direct current, thereby electrodepositing resin particles on and in the anodized oxide film by electrophoresis, and heating the article to cure the resin adsorbed and deposited on the porous film.

Thus, this invention has succeeded in providing aluminum articles having excellent corrosion resistance and electrical insulating qualities as compared with one obtained by the conventional process of closing pores by use of a steam or boiling water treatment, as well as good appearance, smoothness and other valuable qualities.

The film produced on the aluminum in the present invention is fundamentally difi'erent from one produced by simply coating an aluminum oxide film with resin solution by a conventional coating process, such as spray coating or dipping in that in the present process the resin grains are moved electrically and adsorbed in and on the oxidized film to fill up the pores as well as be cured and anchored by the closed micropores of the oxidized film.

According to the process of the present invention, small resin grains are permeated into micropores of the oxidized aluminum to obtain a continuous resin film in contact with substantially the whole of the surface of the oxidized film, and said resin is set thermally in the presence of water and ammonia or amines contained in the aqueous dispersion, emulsion or solution of the thermosetting resin, at the same time the structure of the porous oxidized film is changed from 'y- M 0 to y-AI O 'H O (Boehmite). Thus, the openings of all pores narrow to anchor the resin film.

in order to obtain the superior surface having excellent corrosion resistance, the thickness of the oxidized film must be in the range of from about i p. to about 20 1..

if the thickness of the oxidized film is less than 11.4., the desired cohesion between oxidized film and deposited resin layer is lost or reduced, whereas if the thickness is larger than 20 the resin grains cannot penetrate through the whole of the pores and there develops a tendency for the resin layer to peel off from the oxidized film when the article is bent or deformed.

The anodizing conditions in order to obtain an oxidized film having a thickness of from 1 4, to 20p. depend on the electrolyte used.

Although various kinds of electrolytes may be used for anodical oxidization of aluminum, preferred acid electrolytes in order to obtain an oxidized film useful in the present invention are sulfuric acid, oxalic acid, chromic acid and mixed acids such as mixtures of sulfuric acid and oxalic acid; sulfuric acid and citric acid; sulfonic and boric acid; sulfuric acid, chromic acid and boric acid and citric acid, oxalic acid, boric acid and titanic acid.

While conditions of anodical oxidization suitable for obtaining an oxidized film having a thickness of from 1p. to 20p. will in general range from 2 to 20 percent acid concentration, from 15 to 50 C. temperature of electrolyte, from 0.1 to 3 a./dm. initial current density and from 5 to 60 minutes charging time, these conditions are preferably selected with these ranges depending on the particular electrolyte. Preferable conditions for selected acid electrolytes are as follows:

The thermosetting resin used in the present invention may, for example, be an acrylic resin, such as acrylic acid resin, an acrylate resin or acrylamide resin, or a reaction product or a mechanical mixture of an alkyd resin and water-soluble melamine resin or of a vinyl-modified unsaturated alkyd resin and a water-soluble melamine resin, the water-soluble melamine resin being obtained from hexamethylol melamine hexaalkylether. The vinyl modified unsaturated alkyd resins are made by the polymerization of a vinyl monomer with an alkyd resin composed of an unsaturated oil or fatty acid. Herein, by the term vinyl monomer is meant a monomer having a vinyl group (-CH =CH in the molecule, such as an acrylic ester, for example methyl acrylate and ethyl acrylate, a methacrylic ester, for example methyl methacrylate and hydroxyethyl methacrylate, an unsaturated organic acid, for

I example acrylic acid and methacrylic acid, and styrene.

The above-mentioned thermosetting acrylic resins may be made by heating and stirring a mixture consisting of organic solvents such as methanol, ethylene glycol monobutyl ether and/or cyclohexanone, unsaturated organic acids such as acrylic acid, methacrylic acid and/or maleic anhydride, a cross-linking vinyl monomer (as defined above) such as methylol-acrylamide and/or methylol methacrylamide, a polymerizable vinyl monomer (as hereinabove defined) such as styrene and/or acrylic acid ester, polymerization catalysts such as benzoyl peroxides and/or lauroyl peroxides, and polymerization regulators such as dodecyl mercaptan and/or carbon tetrachloride, to carry out polymerization, thereafter neutralizing the product with, for example, an aqueous solution of ammonia and/or triethylamine to make the resin soluble in water.

Thermosetting resins composed of alkyd resins and watersoluble melamine resin obtained from hexamethylol melamine hexaalkyl ether, may be obtained by mixing a water-soluble melamine resin at a temperature of from room temperature to l00 C. with an alkyd resin modified with a fatty acid, the alkyd resin having an acid value of from 10 to and an oil length of from zero to 80 percent, and being obtained by heating a mixture consisting of (l) a saturated or unsaturated aliphatic acid, (2) ethylene glycol, glycerol, polyethylene glycol, other polyhydric alcohol or an epoxide, (3) adipic acid, sebacic acid, maleic anhydride or other polybasic acid or anhydride, and (4) a small quantity of cyclohexanone, toluene or other organic solvent.

Alternatively the thermosetting resin may be obtained by mixing a water-soluble melamine resin and an alkyd resin from the ester exchange process, the resin being obtained by esterifying a mixture of dehydrated castor oil, an above-mentioned polyhydric alcohol and a small amount of an ester exchanging catalyst such as caustic potash, and thereafter esterifying also an abovementioned polybasic acid or anhydride.

Thennosetting resins consisting of a modified acrylic resin and a water-soluble melamine resin, obtained from hexamethylol melamine hexaalkyl ether, may be obtained by polymerizing by heating and stirring a mixture consisting of organic solvents such as methanol, ethylene glycol monobutyl ether and/or cyclohexanone, unsaturated acids such as acrylic acid and/or methacrylic acid, a vinyl monomer (as hereinabove defined), such as styrene and/or acrylic acid ester, a cross-linking vinyl monomer, if necessary, such as methylol acrylic amide or glycidyl methacrylate and polymerization catalysts and/or polymerization regulators, thereby obtaining a modified acrylic polymer; mixing said modified acrylic polymer with a water-soluble melamine resin, which is obtained from hexamethylol melamine hexaalkyl ether and heating at a temperature under 100 C.; making it soluble in water by neutralizing with, for example, an aqueous solution of ammonia and/or triethylamine or by treating the acrylic polymer with, for example, ammonia and thereafter mixing with water-soluble melamine at ambient temperature.

A thermosetting vinyl modified unsaturated alkyd resin may be obtained by dissolving an unsaturated alkyd resin in methanol, ethylene glycol-monobutyl ether or other suitable organic solvent and performing a graft copolymerization with a mixture consisting of unsaturated organic acid(s) such as acrylic acid and/or methacrylic acid, vinyl monomer(s) such as styrene, methacrylic acid ester and/or acrylic acid ester, cross-linking monomer(s) such as methylol acrylic amide if necessary, and peroxide polymerization catalyst(s) and/or polymerization requlator(s), and thereafter neutralizing the thus obtained vinyl modified unsaturated alkyd resin with an aqueous solution of ammonia, for example, to make it soluble in water.

Further, with regard to the resins composed of vinyl modified unsaturated resin(s) and water-soluble melamine resin(s), obtained from hexamethylol melamine hexaalkyl ether, the thermosetting resins may be obtained by heating and mixing the foregoing vinyl modified unsaturated alkyd resin(s) with said water-soluble melamine resin(s) at a temperature below 100 C.; and making it soluble in water by neutralizing it with, for example, an aqueous solution of ammonia; or they may be obtained by rendering the said vinyl modified unsaturated alkyd resin(s) soluble in water by neutralizing with, for example, an aqueous solution of ammonia, and thereafter mixing it with the water-soluble melamine resin(s) at ambient temperature.

In preparing a dispersion, emulsion or solution of the thermosetting resin, the concentration of the resin is selected depending on the conditions to be employed, but a concentration of resin of from 3 to 40 percent by weight is normally used. The best results are obtained when using a concentration of resin of from 5 to 20 percent by weight and by regulatin g the voltage and the initial current density within a safe and economical range.

In the process of the present invention, it is preferred to wash the porous film of aluminum oxide with cool or hot water immediately after electrolytic oxidation of the aluminum, to dip it in a bath of the above-mentioned resin solution or dispersion together with another electrode, to apply direct current between the aluminum article and the electrode to adsorb the resin on the porous film electrolytically and to thereafter cure the adsorbed resin.

lfit is desired to color the porous film of aluminum oxide, a dyestuff may be adsorbed into the porous film of aluminum oxide prior to the adsorption of resin thereon, or there may be added a water paint to the resin dispersion, emulsion or solution in an amount large enough to color the said resin dispersion, emulsion or solution. Thus, products colored as desired and smooth to touch can be provided. In addition, if heat resistant dyes or pigments are used as colorants, the color of the product will be thermally stable.

The electrophoresis according to the present invention is preferably carried out at a temperature of from 10 to 30 C.

After a long period of electrophoresis, ammonia and amine in the electrophoresis bath will accumulate substantially so that the bath becomes alkaline. In such cases, the electrophoresis bath can be regenerated by heating up to about 50 C. or treatment with an anion exchange resin thereby to remove said ammonia and amine to neutralize the resin dispersion, emulsion or solution. The thus generated liquid can be recycled to the electrophoresis bath after cooling.

As previously indicated, the aluminum article with the oxidized film obtained by said electrolytic oxidation is washed 3 with water and immediately dipped in an aqueous solution or emulsion of said thermosetting resin and a direct current is passed through the article as anode whereby electrodeposition of the resin particles is effected by electrophoresis.

The desirable conditions of electrophoresis are that the resinous liquid has a concentration of 3-40 percent and a temperature of from 10 to 30 C. and the direct current has an initial voltage of 50-300 v. and an initial current density of 50600 ma./dm. and the charging time is l-2 minutes.

The resin electrodeposited on and in the oxide film in the manner mentioned above is baked at a temperature suflicient to cause cross-linking of the thermosetting resin(s). Usually, a suitable temperature is from to 250 C, but a temperature of from to 200 C. is preferred, for a period of from 10 to 60 minutes.

The present invention will be further illustrated by way of the following examples:

EXAMPLE 1 Into a reactor equipped with an agitator, a thermometer and a reflux condenser, 42.5 parts of butyl cellosolve and 44.5 parts of methanol were fed and heated at 70 C. While maintaining a reflux temperature of 70 C., 5.5 parts of methacrylic acid, 25 parts of ethyl acrylate, 44.5 parts of methyl methacrylate, five parts of styrene, 1.5 parts of benzoyl peroxide and one part of dodecyl mercaptan were mixed together and fed into the reactor together with 20 parts of methylol acrylamide, in five portions at half-hourly intervals. The reactants were than heated and agitated for four hours reflux at the same temperature. After the conclusion of the reaction, the contents were cooled to 60 C. The acid component was neutralized with 28 percent ammonia water, and the reaction product was diluted with water until the solid matter content was 30 percent.

There was thus obtained a water-soluble resin solution which is dilutable with water freely. This resin solution was diluted with water until the solid matter content was 10 percent and a resin solution for the electrodeposition was made therefrom.

An aluminum plate was degreased and washed and then electrolytically oxidized at 20 C, for one hour by using an electrolyte containing 15 percent of sulfuric acid and a direct current of 1.5 a./dm. The oxide film thus obtained was 9p, thick. Thereafter, adhering electrolyte was washed off the aluminum plate. This plate was dipped in the above-mentioned resin solution maintained at 20 C. and was made an anode for a source of direct current. A stainless steel plate was utilized as a cathode. The electrolytic treatment was performed for one and a half minutes by passing a direct current with an initial voltage of 180 v. and an initial current density of 500 ma./dm.2. The product was then taken from the bath, washed lightly to remove the adhering excess resin and baked at 200 C. for 30 minutes. Thus, an aluminum article with excellent durability against corrosion was obtained.

EXAMPLE 2 Into a reactor equipped with an agitator, a thermometer and a reflux condenser attached with a blowing inlet for nitrogen gas and a separating tube, 332 parts of soybean oil, 120 parts of glycerol and 0.2 parts of sodium methylate were fed. While blowing nitrogen gas in, the ester-exchanging reaction was carried out at a temperature between 230 and 240 C. for 2 hours. After cooling, 222 parts of phthalic anhydride and 50 parts of cyclohexanone were added and esterified at a temperature of between 180 and 210 C. to produce an alkyd resin with an acid value of 50. To 100 parts of alkyd resin, 40 parts of butyl cellosolve were added. Then, it was neutralized with 28 percent ammonia water and diluted with water until the solid matter content became 30 percent. In this way, a resin solution freely miscible with water was obtained. This water-soluble resin solution was mixed with a water-soluble melamine resin at a ratio of solid matter content of 1:1. The mixture was diluted with water up to percent of the gross solid matter content to make a resin solution for electrodeposition.

An aluminum plate was degreased and washed and then electrolytically oxidized at C. for 30 minutes by using an electrolyte containing 15 percent of sulfuric acid and a current density of 3 a./dm. The oxide film thus obtained was 15p thick. Thereafter adhering electrolyte was washed off the aluminum plate. In the manner similar to that used in Example 1, it was treated with a direct current at a voltage of 150 v. and an initial current density of 400 ma./dm. for one minute in the above-mentioned resin solution. The product was then taken from the bath, washed lightly to remove the adhering excess resin and baked at 130 C. for 30 minutes. The cross-linking reaction of the resin adsorbed on the surface of the oxide film was carried out during the heating, thereby forming a continuous resin film. Thus, an excellent aluminum article was obtained.

Example 3 Into a reactor equipped with an agitator, a thermometer and a reflux condenser, 50 parts of cellosolve and 37 parts of methanol were fed and heated to initiate the reflux and maintain the reflux condition. Thereafter, to the reactor a mixture of five parts of acrylic acid, five parts of hydroxyethyl acrylate, 20 parts of ethyl acrylate, 45 parts of methyl methacrylate, 5 parts of butyl acrylate, 1.5 parts of benzoyl peroxide and 0.5 parts of dodecyl mercaptan was added in five portions at halfhourly intervals. After conclusion of the feeding, it was heated, and stirred for 5 hours under reflux, and, after conclusion of the reaction, it was cooled. Acid components were rendered neutral with triethylamine, and thereafter the mixture was diluted with water until the solid matter content was 30 percent.

In this manner, a resin solution freely miscible with water was produced. This solution and a water-soluble melamine resin were mixed at a ratio of solid matter content of 1:1 and were reacted together at 80 C. for 1 hour. The product was diluted with water until the gross solid matter content was 15 percent to give a resin solution for electrodeposition.

An aluminum plate was degreased and washed and then electrolytically oxidized at 30 C. for minutes by using an electrolyte containing 7 percent of oxalic acid and a direct current with a current density of 1.5 a./dm. The oxide film thus obtained was 15p. thick. Thereafter, adhering electrolyte was washed off the aluminum plate. This aluminum was treated in the said resin solution held at 10 C. for 2 minutes in a manner similar to that used in example 1 using direct current of voltage 50 v. and an initial current density of 50 ma./dm. The product was taken out from the bath, washed with water to remove the adhering excess resin and baked at 120 C. for 1 hour.

EXAMPLE 4 l. An ester exchange was carried out using 330 parts of safflower oil, 100 parts of glycerol and 0.2 parts of sodium methylate in a manner similar to example 2. Then, an alkyd resin having an acid value of was produced by adding 220 parts of phthalic anhydride.

2. Into a reactor similar to examples 1 and 3, 20 parts of alkyd resin produced in l above, 55 parts of ethyl cellosolve and 32 parts of methanol were fed. Further, a mixture of five parts of methacrylic acid, five parts of hydroxyethyl methacrylate, 40 parts of ethyl acrylate, five parts of styrene and 1.5 parts of benzoyl peroxide and 20 parts of methylol acrylamide were divided into five partitions and added five times every 30 minutes to the contents of reactor at half-hourly intervals, while maintaining the contents of the reactor at the boiling point. Thereafter, it was heated and stirred for 4 hours under reflux. After the reaction finished, the contents of the reaction were cooled. The acid values of methacrylic acid and alkyd resin were rendered neutral with diethylamine. By diluting with water until the content of solid matter was 30 percent, a resin solution freely soluble in water was obtained. The solution was further diluted with water until the solid matter content became 15 percent, and thereby a resin solution for electrodeposition was made. An aluminum plate was degreased and washed and then electrolytically oxidized at 40 C. for 40 minutes by using an electrolyte containing 3 percent of chromic acid and a direct current with a current density of 0.15 a./dm The oxide film thus obtained was 3p. thick. Thereafter, adhering electrolyte was washed off the aluminum plate. This aluminum was treated in the said resin solution maintained at 25 C. with 200 v. of direct current voltage and 300 ma./dm of the initial current density for 1% minutes in a manner similar to example 1. After being taken out of the bath, the aluminum was washed with water to remove adhering excess resin and baked at C. for a half hour.

EXAMPLE 5 1. Into a reactor similar to example 1, 192 parts of trimethylolpropane, 132 parts of sebacic acid, 67 parts of safflower aliphatic acid and eight parts of cyclohexanone were fed and heated to 200 C. to produce, by esterification, an alkyd resin with an acid value of 50.

2. Into a reactor similar to examples 1 and 3, 20 parts of the alkyd resin obtained in (1), 35 parts of cyclohexanone, 13 parts of isopropyl alcohol and 10 parts of methanol were fed. While maintaining the contents of the reactor at their boiling point, a mixture of three parts of methacrylic acid, 40 parts of methyl methacrylate, 42 parts of ethyl acrylate and 1.5 parts of benzoyl peroxide was added thereto in five portions at halfhourly intervals. After the conclusion of the addition, polymerization was continued for 6 hours under reflux. Then, the contents were cooled and triethylamine was added to render the acid value of the alkyd resin and methacrylic acid neutral. By diluting it with water until the content of solid matters was 30 percent, a resin solution freely soluble in water was produced. This resin solution and a water-soluble melamine resin were mixed at the ratio of solid matter content of 1:1 and then diluted with water until the content of solid matter was 15 percent. This solution served as the resin solution for electrodeposition. A degreased and washed aluminum plate was electrolytically oxided at 60 C. for 30 minutes by using as an electrolyte a solution of 40 g. titanic acid potassium oxalate (TiO(C O K) -2H O), 8 g. boric acid (11 80 1 g. citric acid (C O H-H O) and 1.2 g. oxalic acid (COOH 'ZH O in 1 water and a direct current with a current density of 1-3 a./dm. The oxide film thus obtained was 12p. thick. Thereafter, adhering electrolyte was washed off the aluminum plate. This aluminum was treated in the said resin solution maintained at 30 C. with 180 v. of direct current voltage and 600 ma./dm of the initial current density for 1% minutes in a manner similar to example 1. The product was taken out of the bath, washed with water to remove adhering excess resin and baked at C. for a half hour.

EXAMPLE 6 35 parts of cyclohexanone, 13 parts of isopropylalcohol, 10

parts of methanol, 1.5 parts of methacrylic acid, 42 parts of methyl methacrylate, 42 parts of ethyl acrylate and 1.5 parts of benzoyl peroxide in the before-mentioned manner, and was diluted with triethylamine and water.

This emulsion and a water-soluble melamine resin were mixed at a ratio of solid matter content of 1:1 and diluted with water until the total content of the solid matter became 20 percent. This emulsion had excellent stability and a long term storage life and employable as a resin emulsion for electrodeposition.

A degreased and washed aluminum plate was electrolytically oxidized at 20 C. for 10 minutes by using an electrolyte containing 15 percent of sulfuric acid and a direct current with a current density of 1.2 a./dm. The oxide film thus obtained was three thick. Thereafter, adhering electrolyte was washed off the aluminum plate. This aluminum with electrolytically oxidized film was treated in the said resin emulsion with 250 v. of direct current voltage and 20 maJdm. as the initial current density for one minute in a manner similar to example The product was taken out of the bath, washed with water to remove adhering excess resin and baked at 180 C. for a half hour.

The aluminum product treated in the above-mentioned manner was excellent in durability, appearance and feel.

EXAMPLE 7 To the resin solution dispersion, or emulsion mentioned in examples 1 to 6, percent of a red water-soluble dye was added. In this manner colored products with soft appearance were produced.

We claim:

1. A method of treating aluminum to provide aluminum articles having a surface coating of high durability, comprising electrolytically oxidizing said article for 5 to 60 minutes in an acid electrolyte having a concentration of 2 to 20 percent and a temperature of 15 to 50 C., using an initial current density of 0.1 to 3 a./dm. to form a porous oxide film having a thickness of l-20u on the surface of the article; immediately after water washing, dipping said article in an aqueous dispersion, emulsion or solution of a thermosetting resin; passing through said article as anode a direct current having an initial voltage of 50-300 volts and an initial current density of 50-600 ma./dm. thereby electrodepositing resin particles on and in the porous oxide film by electrophoresis to form a resin film, and thereafter simultaneously curing the resin film and narrowing the pores of the oxide film to anchor the resin by heating the article at a temperature of l20250 C. for 10-60 minutes.

2. A method according to claim 1 wherein said electrolyte is an aqueous solution of an acid selected from the group consisting of sulfuric acid, oxalic acid and chromic acid.

3. A method according to claim 1 wherein the concentration of the resin in said aqueous dispersion, emulsion or solution is from 3 to 40 percent.

4. A method according to claim 1 wherein a pigment or dye is incorporated into said resin dispersion, emulsion or solution.

5. A method according to claim 1 wherein the temperature of the resin dispersion, emulsion or solution is preferably maintained at 10-30 C.

6. An aluminum article produced by the method of claim 1.

7. A method of producing an aluminum article having improved durability, comprising anodically oxidizing said article at about 20 C. for about 1 hour in an electrolyte containing about 15 percent sulfuric acid and using a direct current of about 1.5 ma./dm. to form an anodized porous oxide film on the surface thereof; immediately after water washing, dipping said article in an aqueous dispersion, emulsion or solution of a thermosetting resin; passing through said article as anode a direct current having a voltage of 50-100 volts and an initial current density of 200-600 ma./dm. thereby electrodepositing resin particles on and in the anodized porous oxide film by electrophoresis and thereafter simultaneously curing the resin film and narrowing the pores of the oxide film to anchor the resin by heating the article at l20-l 60 C. for 10-60 minutes. I. 

2. A method according to claim 1 wherein said electrolyte is an aqueous solution of an acid selected from the group consisting of sulphuric acid, oxalic acid and chromic acid.
 3. A method according to claim 1 wherein the concentration of the resin in said aqueous dispersion, emulsion or solution is from 3 to 40 percent.
 4. A method according to claim 1 wherein a pigment or dye is incorporated into said resin dispersion, emulsion or solution.
 5. A method according to claim 1 wherein the temperature of the resin dispersion, emulsion or solution is preferably maintained at 10*- 30* C.
 6. An aluminum article produced by the method of claim
 1. 7. A method of producing an aluminum article having improved durability, comprising anodically oxidizing said article at about 20* C for about 1 hour in an electrolyte containing about 15 percent sulphuric acid and using a direct current of about 1.5 ma./dm.2 to form an anodized porous oxide film on the surface thereof; immediately after water washing, dipping said article in an aqueous dispersion, emulsion or solution of a thermosetting resin; passing through said article as anode a direct current having a voltage of 50- 100 volts and an initial current density of 200- 600 ma./dm.2, thereby electrodepositing resin particles on and in the anodized porous oxide film by electrophoresis and thereafter simultaneously curing the resin film and narrowing the pores of the oxide film to anchor the resin by heating the article at 120*- 160* C for 10- 60 minutes. 